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<H1>?C1 #<=> ?C2</H1>
The constraint expression C1 is equivalent to the constraint expression C2.


<DL>
<DT><EM>?C1</EM></DT>
<DD>An arithmetic constraint expression.
</DD>
<DT><EM>?C2</EM></DT>
<DD>An arithmetic constraint expression.
</DD>
</DL>
<H2>Description</H2>
   This constraint states that the constraint expressions C1 and C2
   evaluate to the same truth value, either both true of both false.  If
   this is already the case, it simply succeeds.  Otherwise it is suspended
   and after each domain change that may cause one of the constraint
   expressions to succeed to fail, it is woken and and re-evaluated.
   Subsequently, if one of the constraint expressions is true or false, the
   same truth value is imposed on the other one.

<P>

<H3>Fail Conditions</H3>
   Fails if C1 and C2 are not bothe true or both false.


<H3>Resatisfiable</H3>
   No.
<H2>See Also</H2>
<A HREF="../../lib/fd/HRF-2.html">#\/ / 2</A>, <A HREF="../../lib/fd/HFR-2.html">#/\ / 2</A>, <A HREF="../../lib/fd/HEG-2.html">#=> / 2</A>, <A HREF="../../lib/fd/HRP-1.html">#\+ / 1</A>
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